diff --git a/sympy/functions/elementary/integers.py b/sympy/functions/elementary/integers.py
index baa342eb32..e56257dce2 100644
--- a/sympy/functions/elementary/integers.py
+++ b/sympy/functions/elementary/integers.py
@@ -309,7 +309,7 @@ def _eval(arg):
                 if arg is S.NaN:
                     return S.NaN
                 elif arg is S.ComplexInfinity:
-                    return None
+                    return S.NaN
                 else:
                     return arg - floor(arg)
             return cls(arg, evaluate=False)
